This invention relates to apparatus for smoothing and/or polishing part-spherical surfaces. Such surfaces may be concave or convex. The invention has been developed primary for smoothing and polishing lenses.
Machines which are in use at the present time for smoothing and polishing part-spherical surfaces on lenses each comprise two carriers, one of which is freely rotatable about a first axis and the other of which is rotatable by a motor about a second axis. The lens to be smoothed or polished is mounted on a first of the carriers and the smoothing or polishing tool is mounted on the second of the carriers. The second axis is usually fixed with respect to a base on which the machine stands and the first axis is moved to cause a traversing movement of the tool across the lens and also to maintain proper contact between the working surface of the tool and the surface of the lens which is being smoothed or polished. Traversing of the tool across the lens is necessary to avoid the formation of circular marks on the lens. It is usually desirable to adjust the stroke of the traversing movement when there is a change in the size and/or radius of curvature of the lens surfaces being smoothed or polished. Adjustments of the relative positions of the axes are also necessary so that a considerable proportion of a period which is required to smooth or polish a series of different lenses on a single machine is occupied by adjustment of the machine.
It is necessary for the lens and tool to be urged together resiliently, since some movement of the respective carriers or associated supporting parts towards and away from each other is necessary as the tool traverses across the lens face. Since the lens is not positively held in the machine, there is a possibility of a lens moving completely off the tool during operation. The risk of this occurring increases with increasing speed of operation. For this reason, rotation about the second axis is normally limited to a value in the region of 550 rpm.